I have a native Spanish upper intermediate srudent. He has some problems with s and sh, although both these exist in his first language.
However, the z sound does not. Any tips for how to explain how to make this sound?
Also, he tends to lack clarity in the difference with n and m at the end of consonants.

Finally - pronouncing /id/ at the end of verbs such as waited and applauded - this is easy enough but much harder to clearly explain the difference in pron. of /t/ at the end of smoked, and /d/ at the end of climbed.

I've tried to teach the 'voiced/unvoiced' explanation but is there a sumpler way to get this across?

Any suggestions gratefully received, also which are the best books to buy to help my studies on pronunciation. I'm about to start a DELTA and pre-course reading should include phonology I guess?